The work outlined in this grant involves elucidating the biologic importance of a secreted platelet protein - Platelet Factor Four - and developing ways to study Platelet Factor Four levels in patients with thrombotic disorders. Studies to date have shown that Platelet Factor Four secretion is linked to thrombin generation in clotting whole blood. Platelet Factor Four levels are elevated in patients with thrombosis and vascular disease. Platelet Factor Four levels are transiently elevated during exercise-induced ischemia in patients with coronary artery disease. Platelet Factor Four levels can be lowered by the administration of suitable combinations of antiplatelet drugs. Biochemical studies have shown that PF-4 binds to heparin with very high affinity and forms a four-to-one complex. PF-4 is capable of stripping heparin bound to antithrombin and thus inhibiting heparin's anticoagulant activity. Future studies will investigate the role of the proteoglycan carrier of PF-4. We will also develop techniques to iodinate heparin and study its interaction directly with PF-4. We will also chemically characterize the proteoglycan carrier and compare its interaction with PF-4 to that of heparin. Clinical studies will be carried out involving patients with diabetes, peripheral vascular disease, and pulmonary embolism as well as follow-up studies on the angina pectoris patients to determine the efficacy of measuring PF-4 in various clinical thrombotic states.